Electrosurgical apparatus

ABSTRACT

An electrosurgical apparatus having a feed structure comprising a radiofrequency (RF) channel for conveying RF electromagnetic (EM) radiation from an RF signal generator to a probe and a microwave channel for conveying microwave EM radiation from a microwave signal generator to the probe, wherein the RF channel and microwave channel comprise physically separate signal pathways, wherein the feed structure includes a combining circuit having an input connected to the signal pathway on the RF channel, another input connected to the signal pathway on the microwave channel, and an output connected to a common signal pathway for conveying the RE EM radiation and EM radiation separately or simultaneously to the probe, and wherein the microwave channel includes a waveguide isolator connected to isolate the signal pathway on the microwave channel from the RF EM radiation.

FIELD OF THE INVENTION

The invention relates to electrosurgical apparatus in whichradiofrequency energy and microwave frequency energy are used to treatbiological tissue. In particular, the invention relates to surgicalapparatus capable of generating radiofrequency (RF) energy for cuttingtissue and microwave frequency energy for haemostasis (i.e. sealingbroken blood vessels by promoting blood coagulation).

BACKGROUND OF THE INVENTION

Surgical resection is a means of removing sections of organs from withinthe human or animal body. Such organs may be highly vascular. Whentissue is cut (divided or transected) small blood vessels calledarterioles are damaged or ruptured. Initial bleeding is followed by acoagulation cascade where the blood is turned into a clot in an attemptto plug the bleeding point. During an operation, it is desirable for apatient to lose as little blood as possible, so various devices havebeen developed in an attempt to provide blood free cutting. Forendoscopic procedures, it is also undesirable for a bleed to occur andnot to be dealt with as soon as quickly as possible, or in an expedientmanner, since the blood flow may obscure the operator's vision, whichmay lead to the procedure needing to be terminated and another methodused instead, e.g. open surgery.

Instead of a sharp blade, it is known to use radiofrequency (RF) energyto cut biological tissue. The method of cutting using RF energy operatesusing the principle that as an electric current passes through a tissuematrix (aided by the ionic contents of the cells), the impedance to theflow of electrons across the tissue generates heat. When a pure sinewave is applied to the tissue matrix, enough heat is generated withinthe cells to vaporise the water content of the tissue. There is thus ahuge rise in the internal pressure of the cell, that cannot becontrolled by the cell membrane, resulting in the cell rupturing. Whenthis occurs over a wide area it can be seen that tissue has beentransected.

Whilst the above principle works elegantly in lean tissue, it is lessefficient in fatty tissue because there are fewer ionic constituents toaid the passage of electrons. This means that the energy required tovaporise the contents of the cells is much greater, as the latent heatof vaporisation of fat is much greater than that of water.

RF coagulation operates by applying a less efficient waveform to thetissue, whereby instead of being vaporised, the cell contents are heatedto around 65° C. This dries out the tissue by desiccation and alsodenatures the proteins in the walls of vessels and the collagen thatmakes up the cell wall. Denaturing the proteins acts as a stimulus tothe coagulation cascade, so clotting is enhanced. At the same time thecollagen in the wall is denatured and changes from a rod like moleculeto a coil, which causes the vessel to contract and reduce in size,giving the clot an anchor point, and a smaller area to plug.

However, RF coagulation is less efficient when fatty tissue is presentbecause the electrical effect is diminished. It can thus be verydifficult to seal fatty bleeders. Instead of having clean white margins,the tissue has a blackened, burned appearance.

In practice, a RF device may operate using a waveform with a mediumcrest factor that is midway between a cutting and coagulating output.

GB 2 486 343 discloses a control system for an electrosurgical apparatusin which the energy delivery profile of both RE energy and microwaveenergy delivered to a probe is set based on sampled voltage and currentinformation of RF energy conveyed to the probe and sampled forward andreflected power information for the microwave energy conveyed to andfrom the probe.

FIG. 1 shows a schematic diagram of an electrosurgical apparatus 400 asset out in GB 2 486 343. The apparatus comprises a RF channel and amicrowave channel. The RF channel contains components for generating andcontrolling an RF frequency electromagnetic signal at a power levelsuitable for treating (e.g. cutting or desiccating) biological tissue.The microwave channel contains components for generating and controllinga microwave frequency electromagnetic signal at a power level suitablefor treating (e.g. coagulating or ablating) biological tissue.

The microwave channel has a microwave frequency source 402 followed by apower splitter 424 (e.g. a 3 dB power splitter), which divides thesignal from the source 402 into two branches. One branch from the powersplitter 424 forms a microwave channel, which has a power control modulecomprising a variable attenuator 404 controlled by controller 406 viacontrol signal V₁₀ and a signal modulator 408 controlled by controller406 via control signal V₁₁, and an amplifier module comprising driveamplifier 410 and power amplifier 412 for generating forward microwaveEM radiation for delivery from a probe 420 at a power level suitable fortreatment. After the amplifier module, the microwave channel continueswith a microwave signal coupling module (which forms part of a microwavesignal detector) comprising a circulator 416 connected to delivermicrowave EM energy from the source to the probe along a path betweenits first and second ports, a forward coupler 414 at the first port ofthe circulator 416, and a reflected coupler 418 at the third port of thecirculator 416. After passing through the reflected coupler, themicrowave EM energy from the third port is absorbed in a power dump load422. The microwave signal coupling module also includes a switch 415operated by the controller 406 via control signal V₁₂ for connectingeither the forward coupled signal or the reflected coupled signal to aheterodyne receiver for detection

The other branch from the power splitter 424 forms a measurementchannel. The measurement channel bypasses the amplifying line-up on themicrowave channel, and hence is arranged to deliver a low power signalfrom the probe. In this embodiment, a primary channel selection switch426 controlled by the controller 406 via control signal V₁₃ is operableto select a signal from either the microwave channel or the measurementchannel to deliver to the probe. A high band pass filter 427 isconnected between the primary channel selection switch 426 and the probe420 to protect the microwave signal generator from low frequency RFsignals.

The measurement channel includes components arranged to detect the phaseand magnitude of power reflected from the probe, which may yieldinformation about the material e.g. biological tissue present at thedistal end of the probe. The measurement channel comprises a circulator428 connected to deliver microwave EM energy from the source 402 to theprobe along a path between its first and second ports. A reflectedsignal returned from the probe is directed into the third port of thecirculator 428. The circulator 428 is used to provide isolation betweenthe forward signal and the reflected signal to facilitate accuratemeasurement. However, as the circulator does not provide completeisolation between its first and third ports, i.e. some of the forwardsignal may break through to the third port and interfere with thereflected signal, a carrier cancellation circuit is used that injects aportion of the forward signal (from forward coupler 430) back into thesignal coming out of the third port (via injection coupler 432). Thecarrier cancellation circuit include a phase adjustor 434 to ensure thatthe injected portion is 180° out of phase with any signal that breaksthrough into the third port from the first port in order to cancel itout. The carrier cancellation circuit also include a signal attenuator436 to ensure that the magnitude of the injected portion is the same asany breakthrough signal.

To compensate for any drift in the forward signal, a forward coupler 438is provided on the measurement channel. The coupled output of theforward coupler 438 and the reflected signal from the third port of thecirculator 428 are connected to respective input terminal of a switch440, which is operated by the controller 406 via control signal V₁₄ toconnect either the coupled forward signal or the reflected signal to aheterodyne receiver for detection.

The output of the switch 440 (i.e. the output from the measurementchannel) and the output of the switch 415 (i.e. the output from themicrowave channel) are connect to a respective input terminal of asecondary channel selection switch 442, which is operable by thecontroller 406 via control signal V₁₅ in conjunction with the primarychannel selection switch to ensure that the output of the measurementchannel is connected to the heterodyne receiver when the measurementchannel is supplying energy to the probe and that the output of themicrowave channel is connected to the heterodyne receiver when themicrowave channel is supplying energy to the probe.

The heterodyne receiver is used to extract the phase and magnitudeinformation from the signal output by the secondary channel selectionswitch 442. A single heterodyne receiver is shown in this system, but adouble heterodyne receiver (containing two local oscillators and mixers)to mix the source frequency down twice before the signal enters thecontroller may be used if necessary. The heterodyne receiver comprises alocal oscillator 444 and a mixer 448 for mixing down the signal outputby the secondary channel selection switch 442. The frequency of thelocal oscillator signal is selected so that the output from the mixer448 is at an intermediate frequency suitable to be received in thecontroller 406. Band pass filters 446, 450 are provided to protect thelocal oscillator 444 and the controller 406 from the high frequencymicrowave signals.

The controller 406 receives the output of the heterodyne receiver anddetermines (e.g. extracts) from it information indicative of phase andmagnitude of the forward and/or reflected signals on the microwave ormeasurement channel. This information can be used to control thedelivery of high power microwave EM radiation on the microwave channelor high power RF EM radiation on the RF channel. A user may interactwith the controller 406 via a user interface 452, as discussed above.

The RF channel shown in FIG. 1 comprises an RF frequency source 454connected to a gate driver 456 that is controlled by the controller 406via control signal V₁₆. The gate driver 456 supplies an operation signalfor an RF amplifier 458, which is a half-bridge arrangement. The drainvoltage of the half-bridge arrangement is controllable via a variable DCsupply 460. An output transformer 462 transfers the generated RF signalon to a line for delivery to the probe 420. A low pass, band pass, bandstop or notch filter 464 is connected en that line to protect the RFsignal generator from high frequency microwave signals.

A current transformer 466 is connected on the RE channel to measure thecurrent delivered to the tissue load. A potential divider 468 (which maybe tapped off the output transformer) is used to measure the voltage.The output signals from the potential divider 468 and currenttransformer 466 (i.e. voltage outputs indicative of voltage and current)are connected directly to the controller 406 after conditioning byrespective buffer amplifiers 470, 472 and voltage clamping Zener diodes474, 476, 478, 480 (shown as signals B and C in FIG. 1).

To derive phase information, the voltage and current signals (B and C)are also connected to a phase comparator 482 (e.g. an EXOR gate) whoseoutput voltage is integrated by RC circuit 484 to produce a voltageoutput (shown as A in FIG. 1) that is proportional to the phasedifference between the voltage and current waveforms. This voltageoutput (signal A) is connected directly to the controller 406.

The microwave/measurement channel and RF channel are connected to asignal combiner 114, which conveys both types of signal separately orsimultaneously along cable assembly 116 to the probe 420, from which itis delivered (e.g. radiated) into the biological tissue of a patient.

SUMMARY OF THE INVENTION

The present invention provides an enhancement to the electrosurgicalapparatus disclosed GB 2 486 343. The enhancement concerns thecomponents used to isolate the probe from the mains energy used to powerthe apparatus.

At its most general, the present invention proposes using a waveguideisolator at the junction between the microwave channel and signalcombiner. The waveguide isolator may be configured to perform threefunctions: (i) permit the passage of very high microwave power (e.g.greater than 10 W); (ii) block the passage of RF power; and (iii)provide a high withstanding voltage (e.g. greater than 10 kV).

The invention may provide a capacitive structure at or adjacent thewaveguide that can reduce capacitive coupling across the isolationbarrier. The reduced capacitive coupling may be provided by connectingthe waveguide isolator (in particular the outer conductor of thewaveguide isolator) in series with an additional capacitive component,such as a coaxial isolator. To maintain the reduced capacitive couplingduring operation, the additional capacitive component may have a highbreakdown voltage, e.g. 500 V or more. Thus, the waveguide isolator andadditional capacitive component (e.g. coaxial isolator) may act incombination as a low frequency blocking filter to prevent RF EMradiation from the RF channel from entering the microwave channel.

Alternatively, in a preferred embodiment the capacitive structure may bean integral part of the DC isolation barrier in the waveguide isolatoritself. For example, reduced capacitive coupling can be achieved bydecreasing the capacitance or increasing the capacitive reactance of theisolating gap formed in the outer conductor of the waveguide isolator,e.g. by increasing the thickness of insulating material present in thegap. In this arrangement, the waveguide isolator may include a choke tominimise leakage of microwave power at the gap.

The advantage of using a waveguide isolator as described above is thatit both provides a high withstand voltage and prevents unwantedcapacitive coupling between the conductive parts of the waveguideisolator. Without the reduced capacitive coupling, there is a risk of apatient or user in contact with the waveguide isolator forming part of acurrent path resulting from the capacitive coupling, especially in theouter conductor of the waveguide isolator. Such a risk may affect theability of the apparatus to meet the necessary electrical safetystandards for medical devices (e.g. as set by InternationalElectrotechnical Commission (IEC) standard 60601-2).

The invention effectively increases the capacitive reactance of theisolation component and hence inhibits the capacitive coupling.

According to the invention, there may be provided electrosurgicalapparatus for resection of biological tissue, the apparatus comprising:a radiofrequency (RF) signal generator for generating RF electromagnetic(EM) radiation having a first frequency; a microwave signal generatorfor generating microwave EM radiation having a second frequency that ishigher than the first frequency; a probe arranged to deliver the RF EMradiation and the microwave EM radiation separately or simultaneouslyfrom a distal end thereof; and a feed structure for conveying the RF EMradiation and the microwave EM radiation to the probe, the feedstructure comprising an RF channel for connecting the probe to the RFsignal generator, and a microwave channel for connecting the probe tothe microwave signal generator, wherein the RE channel and microwavechannel comprise physically separate signal pathways from the RF signalgenerator and microwave signal generator respectively, wherein the feedstructure includes a combining circuit having a first input connected tothe separate signal pathway on the RF channel, a second input connectedto the separate signal pathway on the microwave channel, and an outputconnected to a common signal pathway for conveying the RF EM radiationand the microwave EM radiation separately or simultaneously along asingle channel to the probe, and wherein the microwave channel includesa waveguide isolator connected to isolate the separate signal pathway onthe microwave channel from the RF EM radiation.

The waveguide isolator may comprise a conductive input section, aconductive output section which mates with the input section to define awaveguide cavity within a volume enclosed by the input and outputsections, and a DC isolation barrier arranged between the input andoutput sections. The waveguide cavity may be cylindrical. The output onthe common signal pathway may include a signal conductor and a groundconductor, and the feed structure may include a capacitive structurebetween the ground conductor of the output on the common signal pathwayand the conductive input section of the waveguide isolator, thecapacitive structure being arranged to inhibit coupling of the RF EMenergy and leakage of the microwave EM energy.

As mentioned above, in a preferred embodiment the capacitive structuremay be provided by the DC isolation barrier and a microwave choke formedon the input section of the waveguide isolator. Where the inner andouter sections of the waveguide isolator define a cylindrical body, themicrowave choke may comprise an annular channel extending axially fromthe distal end of the inner section of the waveguide isolator. Thechannel may be filled with air or another suitable dielectric. The axiallength of the choke may be a quarter wavelength of the microwave EMenergy (or an odd multiple thereof) in the material (e.g. air) andgeometrical structure of the channel.

The DC isolation barrier itself may include a rigid insulating spacerelement mounted between the inner and outer sections of the waveguideisolator. The spacer element may be formed from an insulating plastic,such as Delrin®. In the waveguide is cylindrical, the spacer element maycomprise an annular sleeve mounted over the distal end of one of theinput or output sections of the waveguide isolator. The outer surface ofthe sleeve may be flush with the outer surface of the input and outputsections.

The axial length of the overlap between the sleeve and the inner and/orouter sections is preferably an odd number of quarter wavelengths(usually one quarter wavelength) at the microwave frequency in thematerial of the sleeve and the structure containing it. The thickness ofthe insulating layer (radial thickness when it is an insulating sleeve)may be selected to be either as thin as possible to minimise microwaveleakage or as thick as necessary to reduce the capacitance to a levelthat provides the required isolation at the frequency of the RF EMenergy. These two requirements are in conflict and it may be that theycannot both be met. In practice, the sleeve may thus comprise either (i)a thin insulating layer, which meets the microwave leakage requirementbut requires an additional capacitive break in series with the outerconductor in order to reduce the capacitance (e.g. the coaxial isolatordiscussed below), or (ii) a thick insulating layer, which meets the RFREM energy isolation requirement, but requires an additional microwavecomponent to achieve the required low microwave leakage (e.g. themicrowave choke discussed above).

The DC isolation barrier may includes additional components. Forexample, the DC isolation barrier may include an insulating film mountedon a portion of the inner surface of the input section at the junctionwith the rigid insulating spacer element. The insulating film may extendaway from the rigid insulating spacer element by a predetermineddistance, e.g. to increase the surface breakdown voltage.

The waveguide isolator allows the combining circuit to floatelectrically, which increases safety. The capacitive structure acts toincrease the capacitive reactance of the combining circuit to reduce therisk of an RF signal escaping down the microwave channel via acapacitive coupling through the waveguide isolator.

In another embodiment, the capacitive structure may comprise anadditional capacitance connected in series with the waveguide isolator.The additional capacitance may be a coaxial isolator. The additionalcapacitance may need to have a high breakdown voltage to cope with thepeak voltages seen within the system. The breakdown voltage of theadditional capacitance may be 1 kV or more, preferably 2 kV or more.

Using the adapted waveguide isolator mentioned above or theseries-connected waveguide isolator and coaxial isolator as a high passfilter may overcome three disadvantages of using a single high frequencycapacitor to provide the necessary isolation. Firstly, it is desirablefor the entire combining circuit to be floating, i.e. without a directpath to ground or the mains power. Thus, both the signal and groundplanes from the microwave channel need to enter the combining circuitcapacitively. The waveguide isolator can provide this property.Secondly, it is desirable to prevent the RF signal from leaking out tothe patient or user through capacitive coupling across the waveguideisolator. The adapted DC isolation barrier described above or thecoaxial isolator can provide the necessary capacitance to increase thecapacitive reactance of the junction and hence inhibit the capacitivecoupling at the first frequency. A coaxial isolator is preferred to anormal capacitor because the RF signal may be supplied as high voltagepulses (e.g. of 5 kV or higher), which is higher than the typicalvoltage breakdown of a normal capacitor. Thirdly, the insertion loss ofthe series arrangement is much lower than for a normal capacitor at thepreferred microwave frequencies disclosed herein (e.g. 5.8 GHz orhigher), which can help to prevent the circuit resonating a certainfrequencies.

The invention may be combined with any or all of the components (eitherindividually or in any combination) described above with reference tothe electrosurgical apparatus 400 as set out in GB 2 486 343. Forexample, the RF channel and microwave channel may include any or all ofthe components of the RF channel and microwave channel respectivelydescribed above.

The separate signal pathway on the RF channel may be isolated from themicrowave EM radiation. The RF channel may therefore include anisolator, e.g. a low pass, band pass, band stop or notch filter,connected between the separate signal pathway on the RF channel and thecombining circuit. The low pass, band pass, band stop or notch filtermay be integrated with the combining circuit. For example, in oneembodiment, the combining circuit may comprise a T-shaped openmicrostrip bi-direction diplexer circuit having a low pass, band pass,band stop or notch filter integrally formed therewith to preventmicrowave EM radiation from leaking out of the first input. The bandstop filter may comprise a plurality of stubs (e.g. two, three or fourstubs) formed on the microstrip line between the first input andT-junction of the diplexer circuit.

However, in a preferred embodiment the combining circuit is integratedwith the waveguide isolator. The separate signal pathway on the RFchannel may terminate at an RF connector which is connected into thewaveguide isolator, whereby the RF signal is directly conveyed to anoutput port of the waveguide isolator. The common signal pathway maythus extend away from the output port of the waveguide isolator. Thus,the output connected to common signal pathway may include an outputprobe mounted on the output section of the waveguide isolator, theoutput probe having a coupling conductor extending into the waveguideisolator to couple the microwave EM energy therefrom. The first inputmay include an RF connector mounted on the waveguide isolator, the RFconnector having a signal conductor that extends into the waveguidecavity to electrically contact the coupling conductor of the outputprobe. The signal conductor may be an insulated conductive wire or rod.The signal conductor may contact the coupling conductor at apredetermined distance from its tip. The distance may be adjustable,e.g. by changing the position of the RF connected with respect to thewaveguide isolator. Preferably the position of the signal conductor isaligned close to an equipotential of the microwave EM energy within themicrowave isolator, so the presence of the RF connector does not affectthe behaviour of the microwave EM energy.

Integrating the combining circuit with the adapted waveguide isolatorprovides a single component which provides the necessarygenerator-to-patient isolation whilst avoiding unwanted RF coupling andmicrowave leakage. In addition this single component obviates the needfor a separate multi-stub (low pass) rejection filter on the RF channel.Moreover, the integrated nature of the component means that theinsertion loss of the device is much lower (there is no microstripboard, fewer interconnections, fewer microwave routing cables, noco-axial isolator). The integrated waveguide isolator is also physicallysmaller and easier to manufacture than the multi-component solution.

The apparatus may include a controller operable to select an energydelivery profile for the RF EM radiation and the microwave EM radiation.Herein, energy delivery profile may mean the shape of the waveform interms of voltage/current and time for the RF energy and power level andtime for the microwave energy. Control of the energy delivery profilecan permit a range of therapeutic applications to be realised.

The apparatus may include an RF signal detector for sampling current andvoltage on the RF channel and generating therefrom a RF detection signalindicative of the phase difference between the current and voltage. Thecontroller may be in communication with the RE signal detector toreceive the RF detection signal and select the energy delivery profilefor the RF EM radiation based on the RF detection signal.

Similarly, the apparatus may include a microwave signal detector forsampling forward and reflected power on the microwave channel andgenerating therefrom a microwave detection signal indicative of themagnitude and/or phase of microwave power delivered by the probe. Thecontroller may be in communication with the microwave signal detector toreceive the microwave detection signal and select the energy deliveryprofile for the microwave EM radiation based on the microwave detectionsignal.

Thus, the system may be configured to provide secure control over theoutput of the electrosurgical apparatus. For example, the apparatus mayenable selection of an energy delivery profile for tissue cutting whichmay comprise delivering continuous wave (CW) RF EM energy with a 400 Vpeak amplitude at a power level of 30 W. The controller may beadjustable (e.g. manually adjustable) to vary the peak amplitude andpower level. Because the RF and microwave EM radiation are monitored,the energy delivered to the tissue can be determined with accuracy. Inanother example, the apparatus may enable selection of an energydelivery profile for coagulation may comprise delivering continuous wave(CW) microwave EM energy at a power level of 25 W. Again, the controllermay be adjustable (e.g. manually adjustable) to vary the power level.

More generally, to achieve tissue cutting in a dry environment, it maybe necessary to deliver a 500 kHz continuous wave sinusoidal waveformwith a peak voltage of amplitude 400 V and a power setting of 40 W,whereas to achieve tissue cutting in a wet environment, it may benecessary to deliver one or more bursts of 500 kHz energy with a peakvoltage of 4000 V with a peak power of 200 W and a duty cycle of 10%,which may be set up in the form whereby the ON time is 10 ms and the OFFtime is 90 ms. This kind of pulsed energy delivery profile may ensurethat the energy is passed to the tissue rather than causing undesirableheating of the surrounding fluid. For efficient tissue coagulation indry tissue, CW microwave power may be delivered into tissue at an RMSpower level of 30 W. For coagulation in a wet environment, the microwavepower may be pulsed, e.g. having a peak power of 100 W with a 30% dutycycle.

Other waveforms that produce desirable therapeutic tissue affects mayinclude a combination of RF and microwave energy delivered in CW andpulsed formats similar to those described above. The RF and microwaveenergy may be delivered simultaneously where the microwave energymodulates the RF energy. For example, a 400 V peak 500 kHz CW RF profilemay be modulated with a 10 W CW 5.8 GHz microwave signal to produce adegree of tissue coagulation during the resection process to reducebleeding when an organ or a section of an organ is being removed.

All waveform parameters may be adjustable by the controller, e.g. via auser interface.

The control system may comprise a dedicated measurement channel, fordelivering energy (preferably microwave energy) at a low power level(e.g. 10 mW or less). The system may thus make available measurementsignals from a channel that is not delivering therapeutic effects, i.e.the waveform or energy delivery into tissue may be controlled based onlow power measurements made using a channel that is not involved indelivering therapeutic tissue effects. The measurement channel may beuse the same source as the microwave channel. The system may beswitchable so that microwave energy is delivered either through themeasurement channel (in a “measurement mode”) or through the microwavechannel (in a “treatment mode”). Alternatively, the microwave channelmay be switchable between a low power mode (for measurement) and a highpower mode (for treatment). In this arrangement a separate measurementchannel is not needed.

The system may be configured to supply energy for cutting andcoagulating tissue simultaneously (e.g. a mixed or blend mode) or may beoperated independently, whereby the RE and microwave energy is deliveredto the probe under manual user control (e.g. based on the operation of afootswitch pedal) or automatically based on measured phase and/ormagnitude information from the RF and/or microwave channel. The systemmay be used to perform tissue ablation and cutting. In the instancewhere microwave and RF energy are delivered simultaneously, either orboth RF and microwave energy returned to the respective generators maybe used at high power or low power to control the energy deliveryprofile. In this instance, it may be desirable to take measurementsduring the OFF time when the energy delivery format is pulsed.

The distal end of the probe may comprise a bipolar emitting structurecomprising a first conductor spatially separated from a secondconductor, the first and second conductors being arranged to act: asactive and return electrodes respectively to convey the RF EM radiationby conduction, and as an antenna or transformer to facilitate radiationof the microwave EM energy. Thus, the system may be arranged to providea local return path for RE energy. For example, the RE energy may passby conduction through the tissue separating the conductors, or a plasmamay be generated in the vicinity of the conductors to provide the localreturn path. RF tissue cutting may be produced by a fixed dielectricmaterial separating the first and second conductors, where the thicknessof the dielectric material is small, i.e. less than 1 mm and thedielectric constant high, i.e. greater than that of air.

The invention may be particularly suitable in gastrointestinal (GI)procedures, e.g. to remove polyps on the bowel, i.e. for endoscopicsub-mucosal resection. The invention may also lend itself to precisionendoscopic procedures, i.e. precision endoscopic resection, and may beused in ear, nose and throat procedures and liver resection.

The first frequency may be a stable fixed frequency in the range 10 kHzto 300 MHz and the second frequency may be a stable fixed frequency inthe range 300 MHz to 100 GHz. The first frequency should be high enoughto prevent the energy from causing nerve stimulation and low enough toprevent the energy from causing tissue blanching or unnecessary thermalmargin or damage to the tissue structure. Preferred spot frequencies forthe first frequency include any one or more of: 100 kHz, 250 kHz, 500kHz, 1 MHz, 5 MHz. Preferred spot frequencies for the second frequencyinclude 915 MHz, 2.45 GHz, 5.8 GHz, 14.5 GHz, 24 GHz. Preferably thesecond frequency is at least an order of magnitude (i.e. at least 10times) higher than the first frequency.

In another aspect, the invention may be expressed as an isolatingcircuit for electrosurgical apparatus for resection of biologicaltissue, the isolating circuit comprising: a combining circuit having afirst input connectable to receive radiofrequency (RF) electromagnetic(EM) radiation having a first frequency from an RF channel, a secondinput connectable to receive microwave EM radiation having a secondfrequency that is higher than the first frequency from a microwavechannel, and an output in communication with the first and second inputsfor conveying the RF EM radiation and the microwave EM radiation to acommon signal pathway, and a waveguide isolator connected to isolate themicrowave channel from the RF EM radiation, wherein the waveguideisolator comprises a conductive input section, a conductive outputsection which mates with the input section to define a waveguide cavitywithin a volume enclosed by the input and output sections, and a DCisolation barrier arranged between the input and output sections,wherein the output from the combining circuit includes a signalconductor and a ground conductor, and wherein the isolating circuitcomprises a capacitive structure between the ground conductor of theoutput from the combining circuit and the conductive input section ofthe waveguide isolator, the capacitive structure being arranged toinhibit coupling of the RF EM energy and leakage of the microwave EMenergy. Features of the combining circuit, waveguide isolator andcapacitive structure described above may also be applicable to thisaspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention are discussed in detail below withreference to the accompanying drawings, in which:

FIG. 1 is an overall schematic system diagram of electrosurgicalapparatus in which the present invention may be used, and is discussedabove;

FIG. 2 is a schematic diagram of an isolating circuit in anelectrosurgical apparatus that is an embodiment of the invention;

FIG. 3 is a schematic diagram of an isolating circuit having only awaveguide isolator, for comparison with the present invention;

FIG. 4 is a schematic diagram of an isolating circuit according to thepresent invention, for comparison with FIG. 3;

FIG. 5 is a cross-sectional side view of a waveguide isolator suitablefor use in the invention;

FIG. 6 is an end view of the waveguide isolator shown in FIG. 5;

FIG. 7 is a cross-sectional side view of a coaxial isolator suitable foruse in the invention;

FIG. 8 is a cross-sectional side view of the components in the coaxialisolator shown in FIG. 7;

FIG. 9 is a schematic diagram of an isolating circuit in anelectrosurgical apparatus that is another embodiment of the invention;

FIG. 10 is a cross-sectional side view of an adapted waveguide isolatorused in the isolating circuit of FIG. 9.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

FIG. 2 is a schematic diagram of an isolating circuit 200 for anelectrosurgical apparatus that is an embodiment of the invention. Theisolating circuit 200 forms part of a feed structure for conveying RF EMradiation from an RF signal generator 218 and microwave radiation from amicrowave signal generator 220 to a probe. In this embodiment, the probe(not shown) is connectable to an output port 228 provided in a housing226. The feed structure comprises an RF channel having a RF signalpathway 212, 214 for conveying the RF EM radiation and a microwavechannel having a microwave signal pathway 210 for conveying themicrowave EM radiation. The signal pathways for the RF EM radiation andmicrowave radiation are physically separate from each other. The RFsignal generator is connected to the RF signal pathway 212, 214 via avoltage transformer 216. The secondary coil of the transformer 216 (i.e.on the probe side of the arrangement) is floating, so there is notdirect current path between the patient and the RF signal generator 218.This means that both the signal conductor 212 and ground conductor 214of the RF signal pathway 212, 214 are floating.

A combining circuit 206 has a first input 203 for connecting to the RFsignal pathway 212, 214, and a second input 205 for connecting to themicrowave signal pathway 210. The combining circuit 206 joins thepathways to an output 207, which is connected to a common signal pathway208. The common signal pathway 208, which may include a flexible cable(e.g. coaxial cable of the like) conveys the RF EM radiation andmicrowave EM radiation to the probe. In this embodiment the combiningcircuit 206 comprises a T-shaped microstrip junction formed on a lowloss microwave dielectric substrate (e.g. a suitable type of RT/Duroid®substrate manufactured by Rogers Corporation). The ground plane of themicrostrip junction, which is formed on the opposite side of thesubstrate from the T-shaped microstrip junction, is connected to theground conductor 214 of the RF signal pathway 212, 214. It is thereforefloating. The T-shaped microstrip junction provides the first input 203,which is connected to the signal conductor 212 of the RF signal pathway.

A band stop filter 222 is provided on the T-shaped microstrip junctionin the form of three stubs 224 in shunt on the microstrip line betweenthe first input 203 and junction 223 with the microwave microstrip line.The stub nearest the junction is spaced from it by an odd multiple of aquarter wavelength of the microwave EM radiation transmitted by themicrostrip. The subsequent stubs are separated from one another by halfthe wavelength. Using more than one stub increase the effectiveness ofthe filter in preventing microwave EM radiation from escaping into theRF pathway 212, 214.

The isolating circuit 200 comprises a waveguide isolator 202 and acoaxial isolator 204 connected in series on the microwave signal pathway210 between the microwave signal generator 220 and second input 205. Thewaveguide isolator 202 and coaxial isolator 204 are effectivelycapacitors acting as high pass filters. They permit microwave EMradiation from the microwave signal generator 220 to pass to thecombining circuit 206, but prevent RE EM radiation from escaping backout of the second input 205 of the combining circuit 206 into themicrowave signal generator 220.

In this embodiment, the microwave channel also include a grounded stub221 having a length equal to an odd multiple of a quarter wavelength ofthe microwave EM radiation transmitted by the microstrip to short outany residual RF EM radiation that does escape through the waveguideisolator and coaxial isolator, whilst keeping the microwave transmissionlosses to a minimum.

The waveguide isolator 202 includes an input port 230 arranged to couplemicrowave EM radiation from the microwave signal generator 220 into thewaveguide cavity of the waveguide isolator 202, and an output port 232arranged to couple microwave EM radiation from the waveguide cavity tothe coaxial isolator 204. The waveguide isolator 202 thus causes boththe signal and ground conductors of the microwave signal pathway 210directed into the coaxial isolator 204 (and hence into the combiningcircuit 206) to be floating.

An insulating sleeve 229 is provided at the output port 228 of thehousing to prevent a current path for connecting the grounded casing ofthe housing with the floating components connected to the output port228. The output port 228 may comprises a Type N screw thread or a quickrelease connector, e.g. to allow different probes to be attached to thehousing.

The waveguide isolator 202 is capable of transferring the microwave EMradiation into the combining circuit 206 and on to the probe with lowlosses while providing sufficient levels of patient protection. Anexample of the waveguide isolator 202 itself is shown FIGS. 5 and 6. Itconsists of a cylindrical waveguide arrangement formed by telescopingtogether a first section 240 with a cooperating second section 242. Eachsection has a connector 248 for coupling microwave EM radiation into orout of the waveguide. For example, each connector 248 may comprise aType N receptacle plug from which an E-field probe extends into thewaveguide cavity to couple microwave energy to or from the cavity.

The inner surfaces of the sections are separated from each other by alayer of dielectric material 246 (in this embodiment an insulation film,e.g. made of Kapton). The outer surfaces are separated by rigidinsulating ring 244, e.g. made of Delrin® plastic. The waveguideisolator 202 thus provides a series capacitor on both the signaltransmission path (i.e. between inner conductors) and between the ground(i.e. outer) conductors.

A cylindrical waveguide is preferred in order to meet the stringentrequirements for the creepage distance and air clearances set by theInternational Electrotechnical Commission (IEC) standard 60601-1. In thepresent invention, the power and voltage levels may require the creepagedistance to be at least 21 mm and the air clearance to be at least 12mm. Other aspects of the geometry of the waveguide are determined asfollows.

The distance between the end walls (which are grounded) and the centreof the E-field probe is preferably a quarter wavelength at the frequencyof the microwave radiation, i.e. to transform a short circuit condition(no E-field) to an open circuit (maximum E-field). The distance betweenthe centres of the two E-field probes is preferably a multiple of a halfa wavelength at the frequency of the microwave radiation, whereby theimpedances will be identical.

The dominant mode of signal propagation (which exhibits the lowestinsertion loss) through a cylindrical waveguide is the TE₁₁ mode. Thediameter D of the waveguide required to enable the signal to propagateis given by

$D = \frac{1.8412\; c}{\pi \; f\sqrt{\mu_{r}\epsilon_{r}}}$

where c is the speed of light in a vacuum, f is the frequency ofoperation, μ_(r) is the relative permeability for a magnetic loadingmaterial (magnetic loading factor), ∈_(r) is the relative permittivityfor an electric loading material (dielectric loading factor), and thefactor 1.8412 comes from the solution of the Bessel function for acylindrical waveguide that supports the dominant TE₁₁ mode ofpropagation and the calculation for the cut-off frequency for lowestinsertion loss at the frequency of operation.

For example, if the structure is not loaded (as is preferred to achievethe lowest insertion loss), the diameter D for the dominant mode topropagate at 5.8 GHz is greater than 30.3 mm. The actual diameter usedmay be chosen to take into account or exclude modes that may propagateat larger diameters. In one embodiment, the diameter is 40.3 mm.

A cylindrical waveguide is ideal for achieving the higher levels ofprotection noted above. However, care is needed to ensure that there isnot too much capacitance across the isolated grounds (outer conductors),which may increase the amount of RF energy coupled between the RF signalpath and the isolated ground, thus increasing the chances of electricshock and burns to the patient. This is illustrated in the comparativeisolator circuit arrangement illustrated in FIG. 3.

In FIG. 3, an RF source 300 and an microwave source 302 (e.g. poweramplifier) are connected to deliver RF energy and microwave energyrespectively to a feed structure. Similarly to FIG. 2, the feedstructure comprises an RF channel 306 for the RF energy and a microwavechannel 304 for the microwave energy. The RF channel 306 and microwavechannel 304 comprises physically separate pathways from their respectivesources. The pathways are joined at a combining circuit 308. The RFchannel 306 includes a voltage transformer 310, which isolates thecombining circuit 308 from the RF source 300. The microwave channel 304includes a waveguide isolator 312, which isolates the combining circuit308 from the microwave source 302. Thus, both inner and outer conductorson the RF channel 306 and the microwave channel 304 on the combiningcircuit side of the transformer 310 and waveguide isolator respectivelyare floating, as indicated in FIG. 3 by dotted box 314.

The electrosurgical apparatus of the present invention is preferablycapable of generating an RF signal having a power of 150 W or more.According to IEC 60601, a 150 W RF power generator may allow 1% (i.e.1.5 Wrms) of the maximum delivered power in a 200Ω resistor leastfavourably connected between RF output and ground. In the comparativeexample shown in FIG. 3, 200Ω resistors were connected between theisolated grounds (output side and generator side) and between theisolated RF output (output side) and isolated ground (generator side).The power dissipated in these resistors was measured using anoscilloscope. The power dissipated in the 200Ω resistor connectedbetween the RF output and isolated ground (generator side) was 4.7 Wrms,which is greater the prescribed IEC 60601 minimum.

In one embodiment, the present invention provides a coaxial isolatorconnected in line with the waveguide isolator, i.e. in series betweenthe waveguide isolator and the combining circuit. The coaxial isolatorconsists of a length of coaxial line with a series capacitor in theouter conductor. Any example of a suitable coaxial isolator 500 is shownin FIGS. 7 and 8. The coaxial isolator 500 comprises an input coaxialconnector 502, which may be a Type N male connector, and an outputcoaxial connector 504, which may be a Type N female connector arrangedopposite one another with a space therebetween.

As shown in more detail in FIG. 8, the inner conductor 503 of the inputconnector 502 and the inner conductor 505 of the output connector 504each have a conductive sleeve 507, 509 mounted on their free ends. Theconductive sleeve 507 of the input connector 502 defines a firstcooperating part (here a recess). The conductive sleeve 509 of theoutput connector 504 defines a second cooperating part (here aprojection) which mates with the first cooperating part. The first andsecond cooperating parts are separated from each other by an insulatinglayer 511 (e.g. of Kapton tape). The insulating layer may have athickness of 0.3 mm or more.

Similarly, the outer conductor 513 of the input connector 502 and theouter conductor 515 of the output connector 504 each have a conductivesleeve 517, 519 mounted on their free ends. The conductive sleeves 517,519 mate with one another. The conductive sleeves 517, 519 are separatedfrom one another by a insulating layer 518 (e.g. of Kapton tape), and arigid insulating spacer element 510 (e.g. of Delrin®).

The effect of the coaxial isolator is illustrated in FIG. 4, which showsan isolating circuit that is an embodiment of the invention having acoaxial isolator 316 connected between the waveguide isolator 312 andthe combining circuit 308. The other components of the circuitcorrespond to those in FIG. 3 and are given the same reference numbers.For this arrangement, the power dissipated in a 200Ω resistor connectedacross the RF output and isolated ground (generator side) is 1.47 Wrms,which meets the requirements of IEC 60601.

The coaxial isolator thus provides for improved patient protection whenthe RF source is energised. Integrating the waveguide isolator andcoaxial isolator in a single arrangement can assist in minimisingmicrowave transmission losses.

FIG. 9 is a schematic diagram showing another embodiment of an isolatingcircuit for an electrosurgical apparatus. Features in common with theembodiment of FIG. 2 are given the same reference numbers and are notdescribed again. In this embodiment, the isolating circuit comprises awaveguide isolator 600 whose insulating gap is configured to provide thenecessary level of DC isolation whilst also having an capacitivereactance that is high enough at the frequency of the RF energy toprevent coupling of RE energy across the insulating gap and low enoughat the frequency of the microwave energy to prevent leakage of themicrowave energy at the gap. The configuration of the gap is explainedin detail with reference to FIG. 10. This configuration means that thecoaxial isolator used in the embodiment of FIG. 2 is not needed.

In addition, in this embodiment the combining circuit is integrated withthe waveguide isolator 600. The signal conductor 212 and groundconductor 214 carrying the RF signal are connected to a coaxial RFconnector 602, which introduces the RF signal into the waveguideisolator 600, from where it is conveyed out from the output port 232towards the probe. The isolating gap 603 is arranged to prevent the RFsignal from coupling back into the input port 230. Microwave energy isprevented from coupling into the RF connector 602 by careful placementof the inner conductive rod within the waveguide isolator, as explainedbelow. Combining the RE and microwave energy in the waveguide isolatorobviates the need of a separate combining circuit, which reduces thenumber of components required for the isolating circuit and enables itto be provided as a more compact unit.

FIG. 10 shows a cross-sectional side view of the adapted waveguideisolator 600 used in the isolating circuit of FIG. 9. Similarly to FIG.5, the waveguide isolator 600 has a cylindrical body made up of twomating parts. In this embodiment, an input section 604 is a femalecomponent having an opening for receiving an output section 606, whichhas a cooperating male component. An input port 230 and an output port232 are mounted on the input section 604 and output section 606respectively in the same way as FIG. 5.

The DC gap, which insulates the input section 604 from the outputsection 606 comprises a number of component parts. The component partsall have rotational symmetry around the axis of the cylindrical body. Afirst component part is a primary insulating ring 608, e.g. made ofrigid material such as Delrin® plastic, which surrounds the malecomponent of the output section 606 and separates (and electricallyisolates) the outer surfaces of the input section 604 and output section606.

The axial length of the insulating ring 608 is shorter than the malecomponent of the output section 606, so that a length of the malecomponent extends beyond the distal end of the insulating ring 608. Thissection of the male component overlaps with the distal end of the femalecomponent of the input section 604. A second component part of the DCgap is a secondary insulating ring 612 (which may be formed in one piecewith the primary insulating ring 608) which provide a radial insulationbetween the distal ends of the male and female components.

A third component part of the DC gap is an insulating film 610 (e.g. oneor more layers of Kapton® tape) which cover the inside surface of theinput section 604 for an axial length beyond the distal end of theoutput section 606. The insulating film can isolate the input sectionfrom any fringing fields at the distal end of the output section 606.

A fourth component part of the DC gap is an air-filled microwave choke614, which is a narrow annular channel in the distal end of the inputsection 604. The presence of the microwave choke 614 lowers thecapacitive reactance at the frequency of the microwave energy, whichprevents leakage (e.g. radiation) of the microwave energy at the DC gap.

The increased complexity of the DC gap configuration in this embodimentincreases the capacitive reactance at the frequency of the RF energy bywidening the ‘average’ gap between the input and output sections.Meanwhile the presence of the microwave choke 614 makes use of resonanteffects to ensure that the capacitive reactance at the frequency of themicrowave energy is low enough to avoidance leakage of microwave energyfrom the gap.

In this embodiment, the waveguide isolator also acts as the combiningcircuit. The RF connector 602 has an inner conductive rod 616 thatprojects into the waveguide isolator, where it meets the inner conductor618 of the coaxial output probe (output port 232) at a point spaced fromthe end of the inner conductor 618. Moreover, the position of the innerconductive rod is selected to lie substantially parallel to theequipotentials of the microwave energy in the waveguide isolator so thatit does not couple any significant microwave power. This position can bedetermined by known simulation techniques, and may be finely tunedpermitting adjustment of the radial position of the insertion point, orwith a suitable tuning screw.

1. Electrosurgical apparatus for resection of biological tissue, theapparatus comprising: a radiofrequency (RF) signal generator forgenerating RF electromagnetic (EM) radiation having a first frequency; amicrowave signal generator for generating microwave EM radiation havinga second frequency that is higher than the first frequency; a probearranged to deliver the RF EM radiation and the microwave EM radiationseparately or simultaneously from a distal end thereof; and a feedstructure for conveying the RF EM radiation and the microwave EMradiation to the probe, the feed structure comprising an RF channel forconnecting the probe to the RF signal generator, and a microwave channelfor connecting the probe to the microwave signal generator, wherein theRF channel and microwave channel comprise physically separate signalpathways from the RF signal generator and microwave signal generatorrespectively, wherein the feed structure includes a combining circuithaving a first input connected to the separate signal pathway on the RFchannel, a second input connected to the separate signal pathway on themicrowave channel, and an output connected to a common signal pathwayfor conveying the RF EM radiation and the microwave EM radiationseparately or simultaneously along a single channel to the probe,wherein the microwave channel includes a waveguide isolator connected toisolate the separate signal pathway on the microwave channel from the RFEM radiation, wherein the waveguide isolator comprises: a conductiveinput section, a conductive output section which mates with the inputsection to define a waveguide cavity within a volume enclosed by theinput and output sections, and a DC isolation barrier arranged betweenthe input and output sections, wherein the output on the common signalpathway includes a signal conductor and a ground conductor, and whereinthe feed structure includes a capacitive structure between the groundconductor of the output on the common signal pathway and the conductiveinput section of the waveguide isolator, the capacitive structure beingarranged to inhibit coupling of the RF EM energy and leakage of themicrowave EM energy.
 2. Electrosurgical apparatus according to claim 1,wherein the capacitive structure is provided by the DC isolation barrierand a microwave choke formed on the input section of the waveguideisolator.
 3. Electrosurgical apparatus according to claim 2, wherein theinner and outer sections of the waveguide isolator define a cylindricalbody, and wherein the microwave choke comprises an annular channelextending axially from the distal end of the inner section of thewaveguide isolator.
 4. Electrosurgical apparatus according to claim 1,wherein the DC isolation barrier includes a rigid insulating spacerelement mounted between the inner and outer sections of the waveguideisolator.
 5. Electrosurgical apparatus according to claim 4, wherein theDC isolation barrier includes an insulating film mounted on a portion ofthe inner surface of the input section at the junction with the rigidinsulating spacer element.
 6. Electrosurgical apparatus according toclaim 5, wherein the insulating film extends away from the rigidinsulating spacer element by a predetermined distance. 7.Electrosurgical apparatus according to claim 1, wherein the capacitivestructure includes a coaxial isolator connected in series with thewaveguide isolator.
 8. Electrosurgical apparatus according to claim 7,wherein the coaxial isolator has a breakdown voltage of 500 V or more.9. Electrosurgical apparatus according to claim 7, wherein the coaxialisolator comprises an input coaxial connector, an output coaxialconnector arranged opposite and spaced from the input coaxial connector,wherein inner conductors of the input and output connectors and outerconductors of the input and output connectors are insulated from eachanother.
 10. Electrosurgical apparatus according to claim 1, wherein thecombining circuit comprises a microstrip diplexer circuit. 11.Electrosurgical apparatus according to claim 10, wherein the RF channelincludes a low pass, band pass, band stop or notch filter connectedbetween the separate signal pathway on the RF channel and the combiningcircuit for blocking microwave EM radiation from entering the separatesignal pathway on the RF channel.
 12. Electrosurgical apparatusaccording to claim 11, wherein the low pass, band pass, band stop ornotch filter is integrated with the microstrip diplexer circuit. 13.Electrosurgical apparatus according to claim 1, wherein the first andsecond inputs to and the output from the combining circuit areelectrically floating with respect to the RF signal generator andmicrowave signal generator.
 14. Electrosurgical apparatus according toclaim 1, wherein the microwave channel includes a stub connected inshunt therewith between the microwave signal generator and the waveguideisolator, the stub having an electrical length equal to an odd multipleof a quarter wavelength of the microwave EM radiation. 15.Electrosurgical apparatus according to claim 1, wherein the combiningcircuit is located in a housing, and the probe is connectable to anoutput port formed in the housing.
 16. Electrosurgical apparatusaccording to claim 15 having an insulating sleeve at the output port ofthe housing to isolate the housing from the combining circuit.
 17. Anisolating circuit for electrosurgical apparatus for resection ofbiological tissue, the isolating circuit comprising: a combining circuithaving a first input connectable to receive radiofrequency (RF)electromagnetic (EM) radiation having a first frequency from an RFchannel, a second input connectable to receive microwave EM radiationhaving a second frequency that is higher than the first frequency from amicrowave channel, and an output in communication with the first andsecond inputs for conveying the RF EM radiation and the microwave EMradiation to a common signal pathway, and a waveguide isolator connectedto isolate the microwave channel from the RF EM radiation, wherein thewaveguide isolator comprises a conductive input section, a conductiveoutput section which mates with the input section to define a waveguidecavity within a volume enclosed by the input and output sections, and aDC isolation barrier arranged between the input and output sections,wherein the output from the combining circuit includes a signalconductor and a ground conductor, and wherein the isolating circuitcomprises a capacitive structure between the ground conductor of theoutput from the combining circuit and the conductive input section ofthe waveguide isolator, the capacitive structure being arranged toinhibit coupling of the RF EM energy and leakage of the microwave EMenergy.
 18. An isolating circuit according to claim 17, wherein thecapacitive structure is provided by the DC isolation barrier and amicrowave choke formed on the input section of the waveguide isolator.19. Electrosurgical apparatus according to claim 18, wherein the innerand outer sections of the waveguide isolator define a cylindrical body,and wherein the microwave choke comprises an annular channel extendingaxially from the distal end of the inner section of the waveguideisolator.
 20. Electrosurgical apparatus according to claim 17, whereinthe DC isolation barrier includes a rigid insulating spacer elementmounted between the inner and outer sections of the waveguide isolator.